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Патент USA US3028759

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United States PatentFO 'ice
1
3,028,749
ULTRASONIC FLUID DENSITY MEASURING
SYSTEM
Walter Wellrowitz, Nixon, ‘NJ., assignor to Gulton
Industries, Inc, Metuchen, N.J., a corporation of New
,
3,028,749
Patented Apr. 10, 1962
2
echo pulse by the transducer 10. Automatic starter 16 is
provided to start transmitter 14a whenever an echo indi
cating voltage is not sensed by the receiver 15. It is
not activated unless there is a reasonably long period of
no-signal. Rate metering circuit 17 measures the rate of
generation of voltage pulses by transmitter 14a and trans
lates this pulse rate into an output voltage proportional
thereto. Rate metering circuit 17‘ is of the type such as
has been described in the aforementioned joint application
My invention relates to ultrasonic ?uid density measur 10 of Hugo E. Dahlke and me. This application also dis
ing systems and in particular to those systems which are
closes the circuitry for the various electrical components
not temperature dependent.
shown in FIG. 2.
The density of ?uids may be obtained acoustically by
In FIGURE 3, the systems of FIGS. 1 and 2 have been
measuring the acoustic impedance of the ?uid system.
combined to form an integrated system. The transmitter
The disadvantage of such a method is that the measure 15 14 is similar to transmitter 14a of FIGURE 2 and it main
ments obtained are temperature dependent because the
tains a constant output voltage amplitude similar to that
term involving the sound velocity is temperature depend
of generator 12 of FIGURE 1. Peak voltmeter circuit
ent. It is an important object of this invention to over
18 is of the type such as has been described in the Radio
come this disadvantage by providing a system wherein
tron Designer’s Handbook at page 119 and serves to
the sound velocity is also measured and the measured 20 measure the voltage across transducer 10. Variable in
impedance value is divided by the sound velocity. The
ductance 11, as in FIG. 1, is connected between the
resulting value is a measure of the ?uid density which is
transmitter 14 and transducer 10. Dividing voltmeter
independent of the sound velocity.
19 is of the type such as is supplied by Edison Electric Co.
A further object of my invention is to provide such a
(Model Number 222-IJ) and it serves to divide a voltage,
system which is simple to operate, maintain and produce. 25 which is proportional to ?uid density multiplied by
These and other objects, advantages and features will
acoustic velocity (pp), by a voltage which is proportional
be apparent during the course of the following descrip
to the velocity (0) of the mechanical vibrations in the
tion when taken in conjunction with the accompanying
?uid involved, thereby making its output display a meas
drawings wherein:
ure of the density (p).
FIGURE 1 is a block schematic diagram of an ultra 30
Broadly, my invention relates to the measurement of
sonic system for measuring the acoustic impedance of the
the density of the ?uid in a closed system by measuring
Jersey
Filed Jan. 26, 1959, Ser. No. 788,947
3 Claims. (Cl. 73-32)
fluid,
the acoustic impedance of the ?uid in the system. > This
approach has an inherent disadvantage, in that, the re
sonic system for measuring the velocity of sound in the
sults obtained are temperature dependent. This is due
35 to the fact that the term involving sound velocity is tem
?uid, and
FIGURE 3 is a block schematic diagram of an ultra
perature dependent. On the other hand, if a simultane
sonic system for measuring the density of the ?uid by
ous measurement of the sound velocity is made when the
FIGURE 2 is a block schematic diagram of an ultra
combining the systems of FIGURES 1 and 2.
In the drawings, wherein, for the purpose of illustra
tion, is shown a preferred embodiment of my invention,
acoustic impedance is measured, the impedance value
may be divided by the sound velocity, leaving a value of
density which is independent of sound velocity and there
the numeral 10 designates a transducer for generating
fore of temperature.
mechanical vibrations in response to an energizing volt
Referring once again to FIG. 1, it will be noted that the
age applied thereto. It may be of any piezoelectric ma
constant output voltage from voltage generator 12 is ap
terial, but I prefer to utilize the ferroelectric ceramics
plied to transducer 10 through variable inductance 11
such as barium titanate, lead titanate-zirconate or any
which is tuned to resonance with ‘the clamped capacitive
45
other such ceramic material with or without additives.
reactance of transducer 10. When this occurs, the voltage
In FIG. 1, a variable inductance 11 is shown connected
across the transducer 10 is proportional to the acoustic
in series between voltage generator 12 and transducer 10
impedance of the ?uid into which the sound waves are
and is adjusted so that its reactance is equal to and oppo
propagated. The acoustic impedance, in turn, is pro
site in sign to the clamped capacitive reactance of trans
portional to the quantity pr: above mentioned.
ducer 10 at the frequency of mechanical resonance of the 50
In FIG. 2 (and FIG. 3) the repetition rate of the
transducer. Generator 12 is an ultrasonic signal voltage
transmitter 14a (and 14) is a measure of the sound
generator of a frequency of the order of, for example,
velocity (c) in the ?uid and so the higher the repetition
one megacycle per second and a constant output voltage
rate, the higher is the sound velocity. As previously
amplitude of the order of 106 volts. Transducer 10 is
indicated, the rate metering circuit 17 serves to produce
af?xed to ?uid container 13 which may be a pipe, tank 55 an output voltage which is proportional to the repetition
or other container for the ?uid whose density is to be
rate and therefore to the sound velocity (c) in the ?uid.
measured.
In the combined system of FIGURE 3, the density of
Transmitter 14a in FIGURE 2 is a voltage pulse trans
the ?uid is measured by the dividing voltmeter 19 which
mitter with a fundamental frequency of, for example, one
divides the output of the peak voltmeter circuit 18 which
megacycle per second and a maximum pulse rate of ap 60 is proportional to the acoustic impedance by the voltage
proximately 10,000 pulses per second such as has been
output of the rate metering circuit 17 which is propor
described in patent application Serial No. 653,675 for
tional to the sound velocity, to thereby obtain a reading
Ultrasonic Liquid Level Gauge which I made jointly with
which indicates the ?uid density. The voltmeter 19 can
Hugo E. Dahlke. Receiver 15 includes a tuned ampli?er
be calibrated directly in density units.
7
and is adapted to respond to the voltage generated by the 65
While I have disclosed my invention in relation to a
reception by the transducer 10 of mechanical echo vibra
speci?c example and in a speci?c embodiment, I do not
tion pulsations re?ected by the pipe walls. The mechani
wish to be limited thereto, for obvious modi?cations will
cal vibration pulsations thus traverse a ?xed path length.
occur to those skilled in the art without departing from
The output of the receiver 15 is connected to transmitter
the spirit and scope of my invention.
14a so that transmitter 14a generates a pulse each time 70 Having thus described my invention, I claim:
receiver 15 senses a voltage indicating the reception of an
1. An ultrasonic ?uid density measuring system com
3,028,749
3
4
prising container means for containing the ?uid whose
density is being measured, transducer means including a
uring means for measuring the pulse rate output of said
transmitting means, and means responsive both to said
capacitive transmitting transducer a?ixed to said container
?rst and second measuring means for providing an indi~
means for transmitting and receiving mechanical vibra
cation of the density of the ?uid.
tions in said ?uid over a ?xed path length, the received
2. An ultrasonic ?uid density measuring system as de
vibrations generating a voltage in said transducer means,
scribed in claim 1 including means for starting the trans
an inductance connected to said transmitting transducer
mitting means automatically when no echo pulsation is
and adjusted so its reactance is equal to the clamped
sensed by said receiving means.
capacitive reactance of said transmitting transducer and
3. An ultrasonic ?uid density measuring system as de
opposite in sign thereto at the mechanical resonance of 10 scribed in claim 1 wherein said last-mentioned means in
the transducer, pulse transmitting means having a con
cludes dividing means responsive to said ?rst and second
stant output voltage amplitude connected to said induct
measuring means for providing an indication of the value
ance to couple energizing voltage pulses through said in
of the voltage across said transmitting transducer divided
ductance to said transmitting transducer and energize the
by the pulse rate of the output of said transmitting means.
same to provide mechanical vibration pulsations in said 15
References Cited in the ?le of this patent
?uid traversing said ?xed path length, receiving means
coupled to said transducer means to receive the voltage
UNITED STATES PATENTS
generated by said transducer means in response to the re
ceived vibrations, said receiving means being connected to
2,869,357
Kritz ________________ __ Ian. 20, 1959
said transmitting means to trigger the same into operation 20 2,889,705
Hanysz et al ___________ __ June 9, 1959
each time a pulse is received by said receiving means to
2,926,522
Kritz ________________ __ Mar. 1, 1960
provide a pulse repetition rate proportional to the trav
FOREIGN PATENTS
erse time of the mechanical vibration pulsation along said
?xed path length, ?rst measuring means for measuring the
1,128,966
France _______________ _._ Ian. 14, 1957
voltage across said transmitting transducer, second meas 25
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